| Abstract|| |
Context (Background): Guided endodontics has various applications, one of which is for calcified canal negotiation. Recently, a new single-tooth template has been fabricated to overcome the drawbacks of bulky guides, which are difficult to use with rubber dam isolation.
Aim: This study aimed to assess the efficacy of the novel single-tooth template for negotiation of pulp canal calcification (PCC) in three-dimensional (3D)-printed resin incisors by comparing substance loss and time taken between incisal endodontic access (IEA) and single-tooth template-guided endodontic access (SGEA).
Methods: Forty-two resin incisor teeth having patent canal in the apical third were used (N = 21/group). They were subcategorized based on operator's experience into senior endodontist (SE), postgraduate (PG), and undergraduate (UG) (n = 7/operator). Canals were negotiated conventionally for IEA and using the single-tooth template for SGEA. Substance loss was calculated from the volume difference between pre- and postoperative cone-beam computed tomography scans. The time taken was also recorded.
Statistical Analysis Used: Statistical analysis was performed using unpaired t-test and one-way analysis of variance test.
Results: Canals were successfully negotiated in 100% and 95% of teeth in the SGEA and IEA groups, respectively. Overall substance loss and time taken were significantly lesser for SGEA for all operators (P < 0.001). In the IEA group, post hoc test showed statistical significance between SE and UG for substance loss (P < 0.05) and SE–UG and PG–UG for time taken (P < 0.05). No significant difference among operators was noted for both parameters in SGEA.
Conclusions: SGEA resulted in significantly lesser substance loss and time taken for canal negotiation in 3D-printed resin incisors with simulated PCC. This was independent of the experience levels of the operator.
Keywords: Guided endodontics; pulp canal calcification; single-tooth template; substance loss; three-dimensional printing
|How to cite this article:|
Vasudevan A, Sundar S, Surendran S, Natanasabapathy V. Tooth substance loss after incisal endodontic access and novel single-tooth template-guided endodontic access in three-dimensional printed resin incisors with simulated pulp canal calcification: A comparative in vitro study. J Conserv Dent 2023;26:258-64
|How to cite this URL:|
Vasudevan A, Sundar S, Surendran S, Natanasabapathy V. Tooth substance loss after incisal endodontic access and novel single-tooth template-guided endodontic access in three-dimensional printed resin incisors with simulated pulp canal calcification: A comparative in vitro study. J Conserv Dent [serial online] 2023 [cited 2023 May 28];26:258-64. Available from: https://www.jcd.org.in/text.asp?2023/26/3/258/376906
| Introduction|| |
Pulp canal calcification (PCC) is characterized by narrowing and obliteration of the pulp space, and commonly occurs due to trauma, caries, restorations, excessive orthodontic forces, aging, and systemic factors.,,,, According to the American Association of Endodontists, endodontic management of PCC falls into the high-difficulty category as it is laborious and time-consuming and may result in procedural errors.
Advancements in technology have led to the advent of three-dimensional (3D) printing that has helped achieve predictable and successful outcomes. 3D-printed surgical templates were initially developed for implant placement and this was later applied to endodontics. “Guided Endodontics” has various applications such as PCC negotiation, targeted endodontic microsurgery, and autotransplantation., 3D-printed static guides are fabricated using cone-beam computed tomography (CBCT) scans, surface scans, and 3D-design software., The guides being used so far for full arch are long, bulky, and difficult to use with rubber dam isolation. Furthermore, a template covering multiple teeth in the arch needs to be fabricated for treating a single tooth, adding to material wastage and cost. Recently, a new single-tooth template has been fabricated to overcome the drawbacks of bulky guides. Its practicality has been tested in some case reports; however, its efficacy for endodontic access opening is yet to be assessed.
Thus, the aim of this study was to assess the effectiveness of the novel single-tooth template by comparing the amount of substance loss and time taken between incisal endodontic access (IEA) and single-tooth template-guided endodontic access (SGEA) for PCC negotiation in resin teeth among operators with varying levels of experience. The null hypothesis (H0) tested was that there was no significant difference between the two groups with regard to the amount of substance loss and time taken.
| Methods|| |
The manuscript of this laboratory study has been written according to the Preferred Reporting Items for Laboratory studies in Endodontology 2021 guidelines [Supplementary Figure S1]. The study was cleared by the Institutional Review Board (XXXX/IRB-XXXII/2019/504).
Fabrication of resin teeth with simulated pulp canal calcification
CBCT scan of a patient's left maxillary central incisor with PCC was obtained from previous records [Figure 1]a. This tooth was segmented out from the rest of the scan [Figure 1]b and exported as a standard tessellation language (STL) file to the haptic simulator software (Geomagic Freeform Plus). The total length of the tooth was 21 mm, with the crown being 9 mm and root being 12 mm. An experienced design engineer from the Center for Technology-Assisted Reconstructive Surgery (CTARS; Chennai, India) helped virtually design a cylindrical canal with prespecified dimensions of 0.6 mm diameter and length 6.5 mm from the apex [Figure 1]c. This digitally modified root canal was aligned three-dimensionally in the apical region to obtain a virtual tooth with simulated PCC which was then 3D-printed using a form 2 stereolithography printer (Formlabs Inc., Somerville, MA, USA).
|Figure 1: Fabrication of resin tooth samples and 3D-printed novel single-tooth template. (a) Patient's pre-existing CBCT of tooth #21 revealing PCC, (b) Segmented tooth #21 as STL file, (c) Simulation of root canal with specific dimensions in apical region, (d) 3D-printed resin tooth with simulated PCC, (e) Pre-clinical set-up of wax jaw model with mounted resin tooth, (f) Projected straight-line access and virtual drill path planning, (g) Virtual template fabrication – opening created on incisal aspect of the template corresponding to drill path, (h) 3D-printed resin single-tooth template|
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The minimum sample size was calculated based on a pilot study (effect size − 2.763, Zp − 90%, α −0.05) to be 5 teeth per intervention. Totally, 42 such resin teeth with identical dimensions of the canal (N = 21 per group) were fabricated [Figure 1]d.
Fabrication of single-tooth template
A maxillary wax jaw model was used to stabilize the tooth samples and the entire assembly was placed in a mannequin to simulate clinical conditions [Figure 1]e. Surface-scanned data of the jaw model with resin tooth were matched and aligned with the modified STL file of the virtual tooth with simulated PCC using Mimics 2.0 Software. STL file manipulation was done using haptics (Geomagic Freeform Plus Software).
The drill path was planned virtually by projecting a straight-line access from the simulated canal to the incisal edge of the tooth and was checked in all 3D aspects [Figure 1]f. A virtual template was positioned over the crown of the tooth, with a guided opening created incisally at the site of the projected drill path [Figure 1]g. The size of this opening (0.8 mm) corresponded to the bur head size (0.7 mm). This template was then 3D-printed using thermoplastic resin. A rubber sleeve was placed along the opening to provide a snug fit during drilling [Figure 1]h.
Pulp canal calcification negotiation
The procedure in each of the groups was performed by three operators with varying levels of experience: a senior endodontist (SE) with over 10 years of experience, a final year postgraduate student (PG), and an undergraduate residency student (UG) (n = 7 per subgroup). PCC negotiation was done under magnification in increments maintaining the orientation of the drills until the patent canal was reached. The tooth was accessed repeatedly through the guided opening of the template in the SGEA group and freehand in the IEA group. The orientation of the burs and the depth of insertion were intermittently verified with radiographs during the procedure in both the groups. A #15 K-file was used to negotiate the canal and patency was confirmed radiographically.
Incisal endodontic access group
Access cavities were initiated with high-speed ½ size round diamond burs at the center of the incisal edge. After 3–4 mm of penetration, Gates Glidden drills #1, #2 (Mani, Inc.) and long-neck carbide bur (Dentsply Sirona, USA) were used on a slow-speed handpiece to drill through the coronal and middle third with intermittent saline irrigation [Figure 2]a and [Figure 2]b.
|Figure 2: (a-c) IEA: (a) Resin tooth without template/guide, (b) Black arrow indicates the size of the access opening using free-hand approach, (c) Segmentation process for postoperative volume calculation; (d-f) SGEA: (d) Resin tooth with single-tooth template positioned, Black arrow indicates the guided opening (e) Black arrow indicates the size of the access opening initiated using the template, (f) Segmentation process for postoperative volume calculation; (a and d) Pre-experiment; (b and e) Intra-experiment; (c and f) Post-experiment. IEA: Incisal endodontic access, SGEA: Single-tooth template-guided endodontic access|
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Single-tooth template-guided endodontic access group
The fit of the template was checked following which a mark was placed through the opening to indicate the exact position of the access cavity. The template was removed and initial entry was gained by high-speed drilling. The template was then repositioned, and subsequent drilling was carried out through the guided opening of the template [Figure 2]d and [Figure 2]e. The same armamentarium was used as in the case of the IEA group for drilling.
All teeth were subjected to CBCT scans (Planmeca, Finland) prior to and after the procedures. High-resolution, limited field of view (FOV) CBCT images (voxel size: 75 μm; FOV: 4 cm × 5 cm) of the samples were thus obtained. The volume of the tooth preoperatively (excluding the canal space) and postoperatively (excluding the prepared drill path and canal space) was calculated using ITK-SNAP Software v. 3.8.0 (Cognitica, Philadelphia, PA, USA) using a semi-automatic segmentation process [Figure 2]c and [Figure 2]f.
Evaluation of substance loss
Substance loss (mm3) = Preoperative volume (mm3) – Postoperative volume (mm3).
Evaluation of time taken
Time was recorded from the start of the procedure until the canal was negotiated.
Shapiro–Wilk test was used to check for normality distribution. Unpaired t-test was used for intergroup comparison of substance loss and time taken between IEA and SGEA. To assess the influence of varying levels of operator experience on substance loss and time taken, a one-way analysis of variance test followed by post hoc Tukey when applicable was used. P <0.05 was considered statistically significant and P < 0.001 was considered highly statistically significant. Statistical analysis of data was done using the Stata/SE 17.0 software (Stata Corporation, College Station, Texas, USA).
| Results|| |
Shapiro–Wilk test showed normal distribution of data. The mean preoperative volume for all samples in both the groups was uniformly 639.7 ± 0.0 mm3. The mean postoperative volume after gaining access to the patent canal was 572.82 ± 12.54 mm3 for IEA and 620.30 ± 2.76 mm3 for SGEA. Successful canal negotiation was possible in 100% and 95% of teeth in the SGEA and IEA groups, respectively. Labial perforation of one sample occurred in IEA when the UG operator performed the procedure. However, the canal was subsequently negotiated successfully in this sample and thus it was included in the overall analysis.
Evaluation of substance loss
Overall intergroup comparison
The mean substance loss was 66.87 ± 12.54 mm3 for IEA and 19.39 ± 2.76 mm3 for SGEA [Table 1]. Overall, there was a highly statistically significant difference (P < 0.001), with the SGEA group having lesser substance loss.
|Table 1: Overall intergroup comparison between incisal endodontic access and single-tooth template-guided endodontic access for substance loss (mm3) and time taken (minutes) and intragroup comparison to assess the influence of operator variability using one-way analysis of variance test|
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Intragroup comparison for operator variability
The mean substance loss for each operator (SE, PG, and UG) is shown in [Table 1] and [Supplementary Figure S2].
Incisal endodontic access
The mean substance loss among the different operators was highest for UG and lowest for SE, with a significant difference between all three operators (P < 0.05). Post hoc Tukey test revealed a statistically significant difference between SE and UG (P < 0.05), while the other paired comparisons were insignificant (P > 0.05) [Table 2].
|Table 2: Post hoc Tukey analysis (after one-way analysis of variance) for incisal endodontic access group|
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Single-tooth template-guided endodontic access
The mean substance loss among the different operators was lowest for SE and highest for UG with no significant difference among the operators (P > 0.05).
Evaluation of time taken
Overall intergroup comparison
The mean time taken was 28.14 ± 4.65 min for IEA and 16.79 ± 1.34 min for SGEA [Table 1]. Overall, there was a highly statistically significant difference (P < 0.001), with the SGEA group taking lesser time.
Intragroup comparison for operator variability
The mean time taken for each operator (SE, PG, and UG) is shown in [Table 1] and [Supplementary Figure S2].
Incisal endodontic access
The mean time taken among the operators was highest for UG and lowest for SE, with a significant difference between all three operators (P < 0.05). Post hoc Tukey test showed a statistically significant difference between SE and UG (P < 0.05), and between PG and UG (P < 0.001) [Table 2].
Single-tooth template-guided endodontic access
The mean time taken among the operators was lowest for SE and highest for UG with no significant difference among the operators (P > 0.05).
| Discussion|| |
Guided endodontics can be performed using either a static or dynamic approach. Static guides used so far for PCC negotiation are either multiple teeth templates covering the entire arch,,,, intracoronal guide for molars, or sleeveless guide for posterior teeth. The challenges with full-arch templates are that they are bulky and difficult to use with rubber dam, especially in the posterior region. The guide's stability and accuracy may be further compromised in partially edentulous individuals. Thus, there is a need for a single-tooth template to overcome these limitations. This is the first study to test the efficacy of a novel single-tooth template to evaluate substance loss for PCC negotiation.
Recently, 3D printing has been used to fabricate tooth samples for in vitro studies and to aid in treatment planning., When compared to extracted natural teeth which vary in tooth anatomy and size, 3D-printed teeth provide a standardized, uniform study setup and do not need disinfection prior to use. In this study, resin teeth with canal dimensions of 0.6 mm × 6.5 mm were used. Although this is slightly larger than that used by Connert et al., it was possible to replicate the same patent canal in all resin teeth samples with the available technology only when these specified dimensions were set.
In order to overcome some shortcomings of the cingulum access commonly used in anteriors, an incisal-shifted approach was chosen in this study. This may be beneficial for PCC negotiation due to the improved straight-line access to the apical third with superior instrumentation ability.,,, Nevertheless, incisal access may be tough to employ in all cases as it has an esthetic drawback.
Initially, “Guided Endodontics” was performed using long-shank drills and burs with larger diameters (1.0–1.5 mm).,, The contact of the bur with the dentinal wall generated more forces at the bur tip predisposing to crack formation and a rise in root surface temperature. “Microguided Endodontics” described by Connert et al. stems from the fact that small diameter burs of 0.80 mm–0.85 mm are used., Reducing the bur diameter from 1.5 mm to 0.85 mm might have a positive effect by minimizing heat generation. Hence, negotiating the canal via a microguided approach using a small bur (0.7 mm) was considered in this study.
The accuracy of guided templates has been tested by various methods such as linear and angular deviation, precision of drilling, and substance loss.,, The preservation of enamel and dentin enables the tooth to behave more favorably to functional loads in the mouth, thereby enhancing tooth stability and longevity. Dentin losses during PCC negotiation can be evaluated in terms of “substance loss,” which in turn translates to tooth fracture loads., The greater the volume of dentin/substance loss, the higher is the stress concentration in the cervical region, and the greater is the susceptibility to fracture., Therefore, the volume of substance loss during PCC negotiation was three-dimensionally quantified using CBCT scans in this study, as opposed to previous two-dimensional (2D) methods, which may not be explicit.
PCC negotiation requires multiple intermittent radiographic verifications to assess the depth of bur penetration and orientation, with at least two multi-angulated radiographs being recommended for each confirmation. This emphasizes the importance of radiography, especially while managing teeth with PCC. Additionally, this can make the procedure elaborate and lengthy. Only two studies have evaluated the time taken for guided PCC negotiation using multi-tooth bulky templates., Hence, in addition to substance loss, the time taken was also assessed in this study.
This study revealed that the overall mean substance loss was significantly lower for SGEA compared to IEA, which is concurrent with earlier studies.,, Thus, H0 was rejected. In vitro studies on PCC negotiation using guides have shown a low deviation angle in the drill path with sufficient precision. Lesser deviation of the drill and its ability to lie relatively centered in the canal when the single-tooth template was used could be credible reasons for minimal tooth substance loss in the SGEA group.
The overall substance loss was found to be 19.39 ± 2.76 mm3 for SGEA. Interestingly, this was much lower than the volume reduction even for narrow teeth like mandibular incisors (26.52 mm3) reported by Loureiro et al. This further emphasizes the benefit of the novel single-tooth template. The lower substance loss in the SGEA group could have also been due to the use of a smaller drill of 0.7 mm, as opposed to the larger drill of 1.3 mm used by Loureiro et al. However, substance loss quantified in this study was marginally higher than that reported previously., Differences in tooth type and volume measurement methods may be possible reasons for this variation.
In this study, a higher substance loss of 66.87 ± 12.54 mm3 was reported in the IEA group. This was more than three times the substance loss that occurred when the novel template was used. This is in accordance with former studies which have all consistently reported a greater volume of hard tissue being sacrificed when the guide is not used,,, owing to the unpredictable, tangentially transported drill path.
It was also found that all samples in the SGEA group had significantly lesser substance loss regardless of the experience levels of the operator, with no untoward events having occurred. Nevertheless, one perforation occurred for the UG operator in the IEA group. This substantiates the fact that the novel template proposed here can be safely, predictably, and reproducibly used, even by less experienced operators.,,,
The time taken to conventionally locate calcified canals was reported to range from 15 min to 1 h, even with the aid of a microscope. Guided endodontics has helped overcome this difficulty to a great extent. The overall time taken to access the canals in the IEA group (28.14 min) was significantly higher than the SGEA group, which is consistent with previous studies., However, the mean time taken for SGEA (16.79 min) was slightly longer than that reported previously., This could be due to the relative newness of the operators to the procedure per se and the extra time between changes of drills. Nonetheless, it is noteworthy that this novel template was beneficial in faster location of calcified canals.
Fabrication of the guided template necessitates a preoperative CBCT scan, which may also be of diagnostic value for PCC and early periapical lesion detection. Although this is not of concern in the current study, extra radiation in the form of a limited FOV CBCT obtained following “as low as reasonably achievable” principles may be justified in clinical research, as it helps reduce chairside time and enhance the accuracy of the treatment provided.
Resin teeth were used to standardize samples and make the preoperative volume uniform. Anyhow, they do not replicate natural tooth substance and may have offered relative “ease in drilling” as compared to natural teeth. Thus, the results of this study need to be extrapolated with caution for an in vivo scenario. Furthermore, due to continual preparation of similar samples, a learning bias could have occurred. However, this was partly overcome by introducing multiple operators. While drilling through the thermoplastic resin of the 3D-printed teeth, optimal cooling of the drill was compromised. Hence, there was more heat generated which caused occasional embedding of the drills within the resin material. In addition, a lot of debris was generated during drilling which clogged the drill path and was challenging to remove. Additionally, this study employed the static method of guided endodontics, restricting its use to straight canals. Due to the rigid nature of the static template, modifying the predefined drill path orientation is unattainable in real time, unlike dynamic navigation.
This is an in vitro study which is the first of its kind, and so the benefits of the novel single-tooth template need to be evaluated in curved canals and posterior teeth. Since the template covers only one tooth, its stability also needs to be checked in upcoming studies. The long-term clinical consequences of a minimally invasive access (SGEA) can limit visibility and adequate debridement of the pulp space and needs further investigation. Furthermore, although in vitro studies have demonstrated that tooth structure preservation is crucial for fracture resistance,,,,, the clinical translation of this is yet to be clarified. Testing the efficacy of this novel template in comparison with dynamically guided procedures is warranted.
| Conclusions|| |
Within the limitations of the present study, SGEA resulted in a significantly lesser amount of substance loss in 3D-printed resin incisors with simulated PCC when compared to IEA. The time taken to negotiate the canals was also significantly lesser when the single-tooth template was used. Substance loss and time taken were lower in the guided access group when the novel template was used, irrespective of the experience levels of the operator.
The authors would like to thank Dr. John Nesan (M. D. S., CTARS, Chennai), Mrs. Joanne (Design Engineer, CTARS, Chennai), and Mr. Sriram Vasudevan (Staff Software Engineer, Machine Learning, LinkedIn, San Francisco) for their valuable technological support.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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Prof. Velmurugan Natanasabapathy
Meenakshi Academy of Higher Education and Research, No. 1, Alapakkam Main Road, Maduravoyal, Chennai - 600 095, Tamil Nadu
Source of Support: None, Conflict of Interest: None
[Figure 1], [Figure 2]
[Table 1], [Table 2]